title: A novel frontal pathway underlies verbal fluency in primary progressive aphasia.
abstract: The frontal aslant tract is a direct pathway connecting Broca's region with the anterior cingulate and pre-supplementary motor area. This tract is left lateralized in right-handed subjects, suggesting a possible role in language. However, there are no previous studies that have reported an involvement of this tract in language disorders. In this study we used diffusion tractography to define the anatomy of the frontal aslant tract in relation to verbal fluency and grammar impairment in primary progressive aphasia. Thirty-five patients with primary progressive aphasia and 29 control subjects were recruited. Tractography was used to obtain indirect indices of microstructural organization of the frontal aslant tract. In addition, tractography analysis of the uncinate fasciculus, a tract associated with semantic processing deficits, was performed. Damage to the frontal aslant tract correlated with performance in verbal fluency as assessed by the Cinderella story test. Conversely, damage to the uncinate fasciculus correlated with deficits in semantic processing as assessed by the Peabody Picture Vocabulary Test. Neither tract correlated with grammatical or repetition deficits. Significant group differences were found in the frontal aslant tract of patients with the non-fluent/agrammatic variant and in the uncinate fasciculus of patients with the semantic variant. These findings indicate that degeneration of the frontal aslant tract underlies verbal fluency deficits in primary progressive aphasia and further confirm the role of the uncinate fasciculus in semantic processing. The lack of correlation between damage to the frontal aslant tract and grammar deficits suggests that verbal fluency and grammar processing rely on distinct anatomical networks.
authors.affiliation: Natbrainlab, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, London, UK. m.catani@iop.kcl.ac.uk
authors.forename: Marco
authors.initials: M
authors.lastname: Catani
authors.forename: Marsel M
authors.initials: MM
authors.lastname: Mesulam
authors.forename: Estrid
authors.initials: E
authors.lastname: Jakobsen
authors.forename: Farah
authors.initials: F
authors.lastname: Malik
authors.forename: Adam
authors.initials: A
authors.lastname: Martersteck
authors.forename: Christina
authors.initials: C
authors.lastname: Wieneke
authors.forename: Cynthia K
authors.initials: CK
authors.lastname: Thompson
authors.forename: Michel
authors.initials: M
authors.lastname: Thiebaut de Schotten
authors.forename: Flavio
authors.initials: F
authors.lastname: Dell'Acqua
authors.forename: Sandra
authors.initials: S
authors.lastname: Weintraub
authors.forename: Emily
authors.initials: E
authors.lastname: Rogalski
mesh_terms: D000368:Aged; D001039:Aphasia, Broca / Q000150:complications / Q000503:physiopathology*; D018888:Aphasia, Primary Progressive / Q000150:complications / Q000503:physiopathology*; D001931:Brain Mapping; D056324:Diffusion Tensor Imaging; D005260:Female; D005625:Frontal Lobe / Q000503:physiopathology*; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D009483:Neuropsychological Tests; D013060:Speech / Q000502:physiology*
keywords: aphasia; dementia; freesurfer; frontal aslant tract; language; tractography; white matter